1. Field of the Invention
This invention relates to the shock mounting of a Direct Access Storage Device and to the use of resilient shock rails to cushion cornets of a Direct Access Storage Device.
2. Description of the Related Art
Personal Computer Memory Card International Association (PCMCIA) standard Direct Access Storage Devices (DASD) are insertable into slots in computers, particularly laptop and notebook computers, where size of the components is a very significant design factor. PCMCIA standard handling specifications require that products (including disk drives) be able to withstand drops onto very hard surfaces. This drop converts a significant amount of potential energy into kinetic energy. Accordingly, due to the reduced size of the disk drive, the PCMCIA DASD is more delicate and may be more susceptible to damage upon impact. The abrupt stop upon impact converts the kinetic energy into very high deceleration forces which may exceed the forces which the PCMCIA DASD components may accommodate.
The rigid structure of the DASD necessary to meet the bending and twisting requirements of the PCMCIA specifications in combination with the relatively hard surface of a vinyl clad cement floor results in a very short duration impact. Very short duration impacts result in deceleration which can exceed the critical acceleration levels for some of the components of the DASD.
Improvement both in the handling characteristics of the device and reduction of the possibility of damage due to impact, will result from either increasing the sturdiness of the internal components, or by reducing the deceleration forces during impact to a point below critical acceleration levels for the components of the DASD. Increasing the sturdiness or the fragility levels of the internal components in some cases is thwarted by the fact that the size of the devices has been reduced to the point wherein maintaining significant strength within some components is no longer possible. An alternative approach to provide shock protection by reducing the deceleration to less than the critical deceleration levels is possible notwithstanding the reduction in size of the devices.
The use of the DASD in laptop and notebook size computers suggests a high probability of DASD impacts as a result of being dropped. The impacts also can partially result from any rough handling of the computer device itself. Additionally, the impact forces could come from dropping the disk drive itself at a time when the DASD is not installed in the computer housing.
Rigid mounting of the DASD within the PCMCIA slot of a computer will pass any impact forces from rough handling of the computer to the internal components of the DASD. Further, dropping the DASD on the floor or other hard surface when the DASD is removed from the computer also will transmit impact forces to the internal components of the DASD.
In both cases, the dropping of the DASD on a hard surface and transmitting impact forces from the computer to the DASD, the cushioning of the DASD at the comers will effectively lengthen the duration of the impact and thus spread over a longer period of time the deceleration necessary to stop the DASD, thereby reducing the deceleration levels. For the PCMCIA Type II form factor, it has been found that the rail corners can protect the drive for approximately 70% of the primary impacts. Because of height constraints which prohibit the padding of the major flat surfaces of the DASD, a 100% protection scheme may not be practical or possible in the PCMCIA Type II form a factor. In laptop or notebook computers, height is a very critical consideration; therefore, a significant shock attenuation pad may not be added to the DASD in such a way as to increase its height correspondingly.
Inasmuch as cushioning at the corners provides a significant amount of impact protection, whenever complete shock attenuation is not possible, comer cushioning becomes the best alternative. In order to be sufficiently shock absorptive, any cushioning material must be highly deformative. The amount of protection afforded by the cushioning will be dependent upon the durometer of the shock absorbing material among other factors; a low durometer material will absorb more force but presents offsetting problems.
An additional requirement of the PCMCIA specification is that the rails be formed to accept keys located in the guide slots of the mating DASD connection, resident within the laptop or notebook computer. The keys, projections within the guide slots, prevent incorrect insertion and connection of the DASD with the connectors within the computer. A use of highly deform able materials in the regions of the corners of the DASD to absorb the impact forces permits deformation of the regions for the keying of the DASD rails required by the PCMCIA specification. Without the keying slots, or if the keying slots are not adequately rigid, the DASD can be forcibly jammed into the mounting guide slots possibly damaging the DASD and/or its connectors. It can be seen that in gaining the advantages of shock mounting, the keying arrangement may be compromised.